Special K can load ReShade through its plugin system, which often have a higher compatibility than loading ReShade through alternative methods.
Be sure to have launched the game at least once with Special K injected into the game.
Close the game if it is currently running.
Open the game-specific config.
Set both SleeplessRenderThread and ShowInVideoCapture to false if they are not already.
Download the official installer of ReShade from https://reshade.me/
Browse to Documents\My Mods\SpecialK\Plugins\ThirdParty\
Create a new folder called ReShade
Move the ReShade installer inside the ReShade folder you just created.
Right click on the Reshade Installer, then select 7-Zip, and then press Extract Here.
Launch the ReShade installer.
Click on [Browse…] and browse to the ReShade installer in the Documents\My Mods\SpecialK\PlugIns\ThirdParty\ReShade folder.
Select the ReShade_Setup installer and then press the Next button.
When asked what API ReShade Setup uses, select any of the Direct3D options (which one does not matter).
Next select all the ReShade effect packages and shaders you want to install. If you want to install a specific ReShade preset from the internet you can usually skip this step.
The previous step should have created a new file called ReShade.ini in the folder. Open the file and add this to the bottom of it:
[APP]
ForceVSync=0
ForceWindowed=0
ForceFullscreen=0
ForceResolution=0,0
Force10BitFormat=0
Start the game.
Press Ctrl + ⇧ Shift + ← Backspace to open the control panel of Special K.
Navigate to Plug-Ins > Third-Party and enable ReShade (Official). Ensure that Plug-In is selected as the load order.
Restart the game a final time, and after the restart press Home to access ReShade’s in-game UI.
If you want to manage the ReShade install, simply run ReShade’s installer and point it to the ReShade installer in Documents\My Mods\SpecialK\PlugIns\ThirdParty\ReShade again as you did in step 7.
It is possible to create separate ReShade presets in ReShades UI which can then be manually switched between when playing different games. Since the ReShade install is shared between all games there is no automated preset switching, so on each launch of a new game the user needs to access ReShade’s in-game UI by pressing Home and manually selecting the appropriate ReShade preset.
ReShade (Custom) refers to a custom fork of ReShade that Kaldaien created back in 2017 and shipped alongside some of his game-specific mods. This fork of ReShade had support for being triggered by Special K before the HUD of games were drawn, allowing the use of custom post-processing shaders without affecting the UI elements of a game.
This fork is outdated and generally not compatible with modern versions of ReShade shaders, and so is not recommended. See the ReShade section above for how to install regular ReShade instead.